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/* |
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* Written by Josh Bloch of Google Inc. and released to the public domain, |
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* as explained at http://creativecommons.org/licenses/publicdomain. |
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*/ |
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|
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package java.util; |
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import java.util.*; // for javadoc (till 6280605 is fixed) |
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import java.io.*; |
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|
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/** |
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* Resizable-array implementation of the {@link Deque} interface. Array |
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* deques have no capacity restrictions; they grow as necessary to support |
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* usage. They are not thread-safe; in the absence of external |
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* synchronization, they do not support concurrent access by multiple threads. |
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* Null elements are prohibited. This class is likely to be faster than |
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* {@link Stack} when used as a stack, and faster than {@link LinkedList} |
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* when used as a queue. |
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* |
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* <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time. |
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* Exceptions include {@link #remove(Object) remove}, {@link |
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* #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence |
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* removeLastOccurrence}, {@link #contains contains}, {@link #iterator |
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* iterator.remove()}, and the bulk operations, all of which run in linear |
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* time. |
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* |
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* <p>The iterators returned by this class's <tt>iterator</tt> method are |
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* <i>fail-fast</i>: If the deque is modified at any time after the iterator |
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* is created, in any way except through the iterator's own <tt>remove</tt> |
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* method, the iterator will generally throw a {@link |
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* ConcurrentModificationException}. Thus, in the face of concurrent |
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* modification, the iterator fails quickly and cleanly, rather than risking |
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* arbitrary, non-deterministic behavior at an undetermined time in the |
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* future. |
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* |
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* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
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* as it is, generally speaking, impossible to make any hard guarantees in the |
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* presence of unsynchronized concurrent modification. Fail-fast iterators |
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* throw <tt>ConcurrentModificationException</tt> on a best-effort basis. |
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* Therefore, it would be wrong to write a program that depended on this |
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* exception for its correctness: <i>the fail-fast behavior of iterators |
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* should be used only to detect bugs.</i> |
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* |
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* <p>This class and its iterator implement all of the |
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* <em>optional</em> methods of the {@link Collection} and {@link |
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* Iterator} interfaces. |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../guide/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @author Josh Bloch and Doug Lea |
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* @since 1.6 |
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* @param <E> the type of elements held in this collection |
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*/ |
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public class ArrayDeque<E> extends AbstractCollection<E> |
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implements Deque<E>, Cloneable, Serializable |
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{ |
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/** |
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* The array in which the elements of the deque are stored. |
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* The capacity of the deque is the length of this array, which is |
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* always a power of two. The array is never allowed to become |
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* full, except transiently within an addX method where it is |
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* resized (see doubleCapacity) immediately upon becoming full, |
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* thus avoiding head and tail wrapping around to equal each |
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* other. We also guarantee that all array cells not holding |
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* deque elements are always null. |
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*/ |
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private transient E[] elements; |
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|
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/** |
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* The index of the element at the head of the deque (which is the |
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* element that would be removed by remove() or pop()); or an |
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* arbitrary number equal to tail if the deque is empty. |
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*/ |
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private transient int head; |
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|
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/** |
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* The index at which the next element would be added to the tail |
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* of the deque (via addLast(E), add(E), or push(E)). |
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*/ |
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private transient int tail; |
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|
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/** |
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* The minimum capacity that we'll use for a newly created deque. |
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* Must be a power of 2. |
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*/ |
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private static final int MIN_INITIAL_CAPACITY = 8; |
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|
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// ****** Array allocation and resizing utilities ****** |
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|
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/** |
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* Allocate empty array to hold the given number of elements. |
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* |
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* @param numElements the number of elements to hold |
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*/ |
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private void allocateElements(int numElements) { |
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int initialCapacity = MIN_INITIAL_CAPACITY; |
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// Find the best power of two to hold elements. |
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// Tests "<=" because arrays aren't kept full. |
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if (numElements >= initialCapacity) { |
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initialCapacity = numElements; |
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initialCapacity |= (initialCapacity >>> 1); |
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initialCapacity |= (initialCapacity >>> 2); |
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initialCapacity |= (initialCapacity >>> 4); |
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initialCapacity |= (initialCapacity >>> 8); |
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initialCapacity |= (initialCapacity >>> 16); |
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initialCapacity++; |
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|
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if (initialCapacity < 0) // Too many elements, must back off |
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initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements |
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} |
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elements = (E[]) new Object[initialCapacity]; |
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} |
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|
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/** |
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* Double the capacity of this deque. Call only when full, i.e., |
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* when head and tail have wrapped around to become equal. |
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*/ |
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private void doubleCapacity() { |
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assert head == tail; |
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int p = head; |
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int n = elements.length; |
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int r = n - p; // number of elements to the right of p |
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int newCapacity = n << 1; |
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if (newCapacity < 0) |
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throw new IllegalStateException("Sorry, deque too big"); |
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Object[] a = new Object[newCapacity]; |
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System.arraycopy(elements, p, a, 0, r); |
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System.arraycopy(elements, 0, a, r, p); |
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elements = (E[])a; |
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head = 0; |
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tail = n; |
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} |
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|
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/** |
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* Copies the elements from our element array into the specified array, |
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* in order (from first to last element in the deque). It is assumed |
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* that the array is large enough to hold all elements in the deque. |
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* |
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* @return its argument |
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*/ |
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private <T> T[] copyElements(T[] a) { |
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if (head < tail) { |
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System.arraycopy(elements, head, a, 0, size()); |
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} else if (head > tail) { |
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int headPortionLen = elements.length - head; |
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System.arraycopy(elements, head, a, 0, headPortionLen); |
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System.arraycopy(elements, 0, a, headPortionLen, tail); |
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} |
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return a; |
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} |
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|
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/** |
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* Constructs an empty array deque with an initial capacity |
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* sufficient to hold 16 elements. |
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*/ |
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public ArrayDeque() { |
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elements = (E[]) new Object[16]; |
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} |
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|
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/** |
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* Constructs an empty array deque with an initial capacity |
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* sufficient to hold the specified number of elements. |
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* |
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* @param numElements lower bound on initial capacity of the deque |
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*/ |
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public ArrayDeque(int numElements) { |
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allocateElements(numElements); |
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} |
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|
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/** |
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* Constructs a deque containing the elements of the specified |
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* collection, in the order they are returned by the collection's |
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* iterator. (The first element returned by the collection's |
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* iterator becomes the first element, or <i>front</i> of the |
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* deque.) |
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* |
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* @param c the collection whose elements are to be placed into the deque |
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* @throws NullPointerException if the specified collection is null |
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*/ |
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public ArrayDeque(Collection<? extends E> c) { |
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allocateElements(c.size()); |
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addAll(c); |
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} |
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|
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// The main insertion and extraction methods are addFirst, |
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// addLast, pollFirst, pollLast. The other methods are defined in |
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// terms of these. |
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|
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/** |
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* Inserts the specified element at the front of this deque. |
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* |
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* @param e the element to add |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public void addFirst(E e) { |
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if (e == null) |
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throw new NullPointerException(); |
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elements[head = (head - 1) & (elements.length - 1)] = e; |
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if (head == tail) |
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doubleCapacity(); |
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} |
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|
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/** |
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* Inserts the specified element at the end of this deque. |
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* |
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* <p>This method is equivalent to {@link #add}. |
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* |
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* @param e the element to add |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public void addLast(E e) { |
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if (e == null) |
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throw new NullPointerException(); |
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elements[tail] = e; |
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if ( (tail = (tail + 1) & (elements.length - 1)) == head) |
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doubleCapacity(); |
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} |
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|
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/** |
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* Inserts the specified element at the front of this deque. |
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* |
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* @param e the element to add |
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* @return <tt>true</tt> (as specified by {@link Deque#offerFirst}) |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean offerFirst(E e) { |
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addFirst(e); |
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return true; |
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} |
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|
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/** |
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* Inserts the specified element at the end of this deque. |
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* |
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* @param e the element to add |
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* @return <tt>true</tt> (as specified by {@link Deque#offerLast}) |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean offerLast(E e) { |
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addLast(e); |
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return true; |
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} |
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|
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/** |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E removeFirst() { |
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E x = pollFirst(); |
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if (x == null) |
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throw new NoSuchElementException(); |
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return x; |
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} |
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|
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/** |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E removeLast() { |
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E x = pollLast(); |
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if (x == null) |
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throw new NoSuchElementException(); |
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return x; |
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} |
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|
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public E pollFirst() { |
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int h = head; |
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E result = elements[h]; // Element is null if deque empty |
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if (result == null) |
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return null; |
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elements[h] = null; // Must null out slot |
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head = (h + 1) & (elements.length - 1); |
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return result; |
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} |
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|
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public E pollLast() { |
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int t = (tail - 1) & (elements.length - 1); |
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E result = elements[t]; |
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if (result == null) |
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return null; |
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elements[t] = null; |
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tail = t; |
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return result; |
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} |
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|
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/** |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E getFirst() { |
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E x = elements[head]; |
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if (x == null) |
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throw new NoSuchElementException(); |
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return x; |
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} |
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|
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/** |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E getLast() { |
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E x = elements[(tail - 1) & (elements.length - 1)]; |
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if (x == null) |
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throw new NoSuchElementException(); |
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return x; |
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} |
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|
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public E peekFirst() { |
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return elements[head]; // elements[head] is null if deque empty |
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} |
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|
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public E peekLast() { |
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return elements[(tail - 1) & (elements.length - 1)]; |
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} |
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|
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/** |
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* Removes the first occurrence of the specified element in this |
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* deque (when traversing the deque from head to tail). |
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* If the deque does not contain the element, it is unchanged. |
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* More formally, removes the first element <tt>e</tt> such that |
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* <tt>o.equals(e)</tt> (if such an element exists). |
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* Returns <tt>true</tt> if this deque contained the specified element |
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* (or equivalently, if this deque changed as a result of the call). |
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* |
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* @param o element to be removed from this deque, if present |
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* @return <tt>true</tt> if the deque contained the specified element |
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*/ |
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public boolean removeFirstOccurrence(Object o) { |
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if (o == null) |
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return false; |
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int mask = elements.length - 1; |
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int i = head; |
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E x; |
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while ( (x = elements[i]) != null) { |
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if (o.equals(x)) { |
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delete(i); |
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return true; |
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} |
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i = (i + 1) & mask; |
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} |
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return false; |
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} |
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|
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/** |
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* Removes the last occurrence of the specified element in this |
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* deque (when traversing the deque from head to tail). |
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* If the deque does not contain the element, it is unchanged. |
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* More formally, removes the last element <tt>e</tt> such that |
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* <tt>o.equals(e)</tt> (if such an element exists). |
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* Returns <tt>true</tt> if this deque contained the specified element |
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* (or equivalently, if this deque changed as a result of the call). |
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* |
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* @param o element to be removed from this deque, if present |
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* @return <tt>true</tt> if the deque contained the specified element |
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*/ |
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public boolean removeLastOccurrence(Object o) { |
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if (o == null) |
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return false; |
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int mask = elements.length - 1; |
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int i = (tail - 1) & mask; |
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E x; |
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while ( (x = elements[i]) != null) { |
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if (o.equals(x)) { |
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delete(i); |
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return true; |
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} |
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i = (i - 1) & mask; |
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} |
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return false; |
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} |
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|
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// *** Queue methods *** |
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|
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/** |
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* Inserts the specified element at the end of this deque. |
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* |
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* <p>This method is equivalent to {@link #addLast}. |
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* |
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* @param e the element to add |
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* @return <tt>true</tt> (as specified by {@link Collection#add}) |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean add(E e) { |
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addLast(e); |
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return true; |
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} |
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|
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/** |
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* Inserts the specified element at the end of this deque. |
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* |
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* <p>This method is equivalent to {@link #offerLast}. |
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* |
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* @param e the element to add |
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* @return <tt>true</tt> (as specified by {@link Queue#offer}) |
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* @throws NullPointerException if the specified element is null |
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*/ |
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public boolean offer(E e) { |
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return offerLast(e); |
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} |
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|
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/** |
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* Retrieves and removes the head of the queue represented by this deque. |
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* |
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* This method differs from {@link #poll poll} only in that it throws an |
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* exception if this deque is empty. |
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* |
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* <p>This method is equivalent to {@link #removeFirst}. |
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* |
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* @return the head of the queue represented by this deque |
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* @throws NoSuchElementException {@inheritDoc} |
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*/ |
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public E remove() { |
409 |
return removeFirst(); |
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} |
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|
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/** |
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* Retrieves and removes the head of the queue represented by this deque |
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* (in other words, the first element of this deque), or returns |
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* <tt>null</tt> if this deque is empty. |
416 |
* |
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* <p>This method is equivalent to {@link #pollFirst}. |
418 |
* |
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* @return the head of the queue represented by this deque, or |
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* <tt>null</tt> if this deque is empty |
421 |
*/ |
422 |
public E poll() { |
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return pollFirst(); |
424 |
} |
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|
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/** |
427 |
* Retrieves, but does not remove, the head of the queue represented by |
428 |
* this deque. This method differs from {@link #peek peek} only in |
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* that it throws an exception if this deque is empty. |
430 |
* |
431 |
* <p>This method is equivalent to {@link #getFirst}. |
432 |
* |
433 |
* @return the head of the queue represented by this deque |
434 |
* @throws NoSuchElementException {@inheritDoc} |
435 |
*/ |
436 |
public E element() { |
437 |
return getFirst(); |
438 |
} |
439 |
|
440 |
/** |
441 |
* Retrieves, but does not remove, the head of the queue represented by |
442 |
* this deque, or returns <tt>null</tt> if this deque is empty. |
443 |
* |
444 |
* <p>This method is equivalent to {@link #peekFirst}. |
445 |
* |
446 |
* @return the head of the queue represented by this deque, or |
447 |
* <tt>null</tt> if this deque is empty |
448 |
*/ |
449 |
public E peek() { |
450 |
return peekFirst(); |
451 |
} |
452 |
|
453 |
// *** Stack methods *** |
454 |
|
455 |
/** |
456 |
* Pushes an element onto the stack represented by this deque. In other |
457 |
* words, inserts the element at the front of this deque. |
458 |
* |
459 |
* <p>This method is equivalent to {@link #addFirst}. |
460 |
* |
461 |
* @param e the element to push |
462 |
* @throws NullPointerException if the specified element is null |
463 |
*/ |
464 |
public void push(E e) { |
465 |
addFirst(e); |
466 |
} |
467 |
|
468 |
/** |
469 |
* Pops an element from the stack represented by this deque. In other |
470 |
* words, removes and returns the first element of this deque. |
471 |
* |
472 |
* <p>This method is equivalent to {@link #removeFirst()}. |
473 |
* |
474 |
* @return the element at the front of this deque (which is the top |
475 |
* of the stack represented by this deque) |
476 |
* @throws NoSuchElementException {@inheritDoc} |
477 |
*/ |
478 |
public E pop() { |
479 |
return removeFirst(); |
480 |
} |
481 |
|
482 |
/** |
483 |
* Removes the element at the specified position in the elements array, |
484 |
* adjusting head and tail as necessary. This can result in motion of |
485 |
* elements backwards or forwards in the array. |
486 |
* |
487 |
* <p>This method is called delete rather than remove to emphasize |
488 |
* that its semantics differ from those of {@link List#remove(int)}. |
489 |
* |
490 |
* @return true if elements moved backwards |
491 |
*/ |
492 |
private boolean delete(int i) { |
493 |
int mask = elements.length - 1; |
494 |
|
495 |
// Invariant: head <= i < tail mod circularity |
496 |
if (((i - head) & mask) >= ((tail - head) & mask)) |
497 |
throw new ConcurrentModificationException(); |
498 |
|
499 |
// Case 1: Deque doesn't wrap |
500 |
// Case 2: Deque does wrap and removed element is in the head portion |
501 |
if (i >= head) { |
502 |
System.arraycopy(elements, head, elements, head + 1, i - head); |
503 |
elements[head] = null; |
504 |
head = (head + 1) & mask; |
505 |
return false; |
506 |
} |
507 |
|
508 |
// Case 3: Deque wraps and removed element is in the tail portion |
509 |
tail--; |
510 |
System.arraycopy(elements, i + 1, elements, i, tail - i); |
511 |
elements[tail] = null; |
512 |
return true; |
513 |
} |
514 |
|
515 |
// *** Collection Methods *** |
516 |
|
517 |
/** |
518 |
* Returns the number of elements in this deque. |
519 |
* |
520 |
* @return the number of elements in this deque |
521 |
*/ |
522 |
public int size() { |
523 |
return (tail - head) & (elements.length - 1); |
524 |
} |
525 |
|
526 |
/** |
527 |
* Returns <tt>true</tt> if this deque contains no elements. |
528 |
* |
529 |
* @return <tt>true</tt> if this deque contains no elements |
530 |
*/ |
531 |
public boolean isEmpty() { |
532 |
return head == tail; |
533 |
} |
534 |
|
535 |
/** |
536 |
* Returns an iterator over the elements in this deque. The elements |
537 |
* will be ordered from first (head) to last (tail). This is the same |
538 |
* order that elements would be dequeued (via successive calls to |
539 |
* {@link #remove} or popped (via successive calls to {@link #pop}). |
540 |
* |
541 |
* @return an <tt>Iterator</tt> over the elements in this deque |
542 |
*/ |
543 |
public Iterator<E> iterator() { |
544 |
return new DeqIterator(); |
545 |
} |
546 |
|
547 |
/** |
548 |
* Returns an iterator over the elements in this deque in reverse |
549 |
* sequential order. The elements will be returned in order from |
550 |
* last (tail) to first (head). |
551 |
* |
552 |
* @return an iterator over the elements in this deque in reverse |
553 |
* sequence |
554 |
*/ |
555 |
public Iterator<E> descendingIterator() { |
556 |
return new DescendingIterator(); |
557 |
} |
558 |
|
559 |
private class DeqIterator implements Iterator<E> { |
560 |
/** |
561 |
* Index of element to be returned by subsequent call to next. |
562 |
*/ |
563 |
private int cursor = head; |
564 |
|
565 |
/** |
566 |
* Tail recorded at construction (also in remove), to stop |
567 |
* iterator and also to check for comodification. |
568 |
*/ |
569 |
private int fence = tail; |
570 |
|
571 |
/** |
572 |
* Index of element returned by most recent call to next. |
573 |
* Reset to -1 if element is deleted by a call to remove. |
574 |
*/ |
575 |
private int lastRet = -1; |
576 |
|
577 |
public boolean hasNext() { |
578 |
return cursor != fence; |
579 |
} |
580 |
|
581 |
public E next() { |
582 |
E result; |
583 |
if (cursor == fence) |
584 |
throw new NoSuchElementException(); |
585 |
// This check doesn't catch all possible comodifications, |
586 |
// but does catch the ones that corrupt traversal |
587 |
if (tail != fence || (result = elements[cursor]) == null) |
588 |
throw new ConcurrentModificationException(); |
589 |
lastRet = cursor; |
590 |
cursor = (cursor + 1) & (elements.length - 1); |
591 |
return result; |
592 |
} |
593 |
|
594 |
public void remove() { |
595 |
if (lastRet < 0) |
596 |
throw new IllegalStateException(); |
597 |
if (delete(lastRet)) |
598 |
cursor--; |
599 |
lastRet = -1; |
600 |
fence = tail; |
601 |
} |
602 |
} |
603 |
|
604 |
|
605 |
private class DescendingIterator implements Iterator<E> { |
606 |
/* |
607 |
* This class is nearly a mirror-image of DeqIterator. It |
608 |
* shares the same structure, but not many actual lines of |
609 |
* code. The only asymmetric part is that to simplify some |
610 |
* checks, indices are anded with length mask only on array |
611 |
* access rather than on each update. |
612 |
*/ |
613 |
private int cursor = tail - 1; |
614 |
private int fence = head - 1; |
615 |
private int lastRet = elements.length; |
616 |
|
617 |
public boolean hasNext() { |
618 |
return cursor != fence; |
619 |
} |
620 |
|
621 |
public E next() { |
622 |
E result; |
623 |
if (cursor == fence) |
624 |
throw new NoSuchElementException(); |
625 |
if ((head - 1) != fence || |
626 |
(result = elements[cursor & (elements.length-1)]) == null) |
627 |
throw new ConcurrentModificationException(); |
628 |
lastRet = cursor; |
629 |
cursor--; |
630 |
return result; |
631 |
} |
632 |
|
633 |
public void remove() { |
634 |
if (lastRet >= elements.length) |
635 |
throw new IllegalStateException(); |
636 |
if (delete(lastRet & (elements.length-1))) |
637 |
cursor++; |
638 |
lastRet = elements.length; |
639 |
fence = head - 1; |
640 |
} |
641 |
} |
642 |
|
643 |
/** |
644 |
* Returns <tt>true</tt> if this deque contains the specified element. |
645 |
* More formally, returns <tt>true</tt> if and only if this deque contains |
646 |
* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>. |
647 |
* |
648 |
* @param o object to be checked for containment in this deque |
649 |
* @return <tt>true</tt> if this deque contains the specified element |
650 |
*/ |
651 |
public boolean contains(Object o) { |
652 |
if (o == null) |
653 |
return false; |
654 |
int mask = elements.length - 1; |
655 |
int i = head; |
656 |
E x; |
657 |
while ( (x = elements[i]) != null) { |
658 |
if (o.equals(x)) |
659 |
return true; |
660 |
i = (i + 1) & mask; |
661 |
} |
662 |
return false; |
663 |
} |
664 |
|
665 |
/** |
666 |
* Removes a single instance of the specified element from this deque. |
667 |
* If the deque does not contain the element, it is unchanged. |
668 |
* More formally, removes the first element <tt>e</tt> such that |
669 |
* <tt>o.equals(e)</tt> (if such an element exists). |
670 |
* Returns <tt>true</tt> if this deque contained the specified element |
671 |
* (or equivalently, if this deque changed as a result of the call). |
672 |
* |
673 |
* <p>This method is equivalent to {@link #removeFirstOccurrence}. |
674 |
* |
675 |
* @param o element to be removed from this deque, if present |
676 |
* @return <tt>true</tt> if this deque contained the specified element |
677 |
*/ |
678 |
public boolean remove(Object o) { |
679 |
return removeFirstOccurrence(o); |
680 |
} |
681 |
|
682 |
/** |
683 |
* Removes all of the elements from this deque. |
684 |
* The deque will be empty after this call returns. |
685 |
*/ |
686 |
public void clear() { |
687 |
int h = head; |
688 |
int t = tail; |
689 |
if (h != t) { // clear all cells |
690 |
head = tail = 0; |
691 |
int i = h; |
692 |
int mask = elements.length - 1; |
693 |
do { |
694 |
elements[i] = null; |
695 |
i = (i + 1) & mask; |
696 |
} while (i != t); |
697 |
} |
698 |
} |
699 |
|
700 |
/** |
701 |
* Returns an array containing all of the elements in this deque |
702 |
* in proper sequence (from first to last element). |
703 |
* |
704 |
* <p>The returned array will be "safe" in that no references to it are |
705 |
* maintained by this deque. (In other words, this method must allocate |
706 |
* a new array). The caller is thus free to modify the returned array. |
707 |
* |
708 |
* <p>This method acts as bridge between array-based and collection-based |
709 |
* APIs. |
710 |
* |
711 |
* @return an array containing all of the elements in this deque |
712 |
*/ |
713 |
public Object[] toArray() { |
714 |
return copyElements(new Object[size()]); |
715 |
} |
716 |
|
717 |
/** |
718 |
* Returns an array containing all of the elements in this deque in |
719 |
* proper sequence (from first to last element); the runtime type of the |
720 |
* returned array is that of the specified array. If the deque fits in |
721 |
* the specified array, it is returned therein. Otherwise, a new array |
722 |
* is allocated with the runtime type of the specified array and the |
723 |
* size of this deque. |
724 |
* |
725 |
* <p>If this deque fits in the specified array with room to spare |
726 |
* (i.e., the array has more elements than this deque), the element in |
727 |
* the array immediately following the end of the deque is set to |
728 |
* <tt>null</tt>. |
729 |
* |
730 |
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
731 |
* array-based and collection-based APIs. Further, this method allows |
732 |
* precise control over the runtime type of the output array, and may, |
733 |
* under certain circumstances, be used to save allocation costs. |
734 |
* |
735 |
* <p>Suppose <tt>x</tt> is a deque known to contain only strings. |
736 |
* The following code can be used to dump the deque into a newly |
737 |
* allocated array of <tt>String</tt>: |
738 |
* |
739 |
* <pre> |
740 |
* String[] y = x.toArray(new String[0]);</pre> |
741 |
* |
742 |
* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
743 |
* <tt>toArray()</tt>. |
744 |
* |
745 |
* @param a the array into which the elements of the deque are to |
746 |
* be stored, if it is big enough; otherwise, a new array of the |
747 |
* same runtime type is allocated for this purpose |
748 |
* @return an array containing all of the elements in this deque |
749 |
* @throws ArrayStoreException if the runtime type of the specified array |
750 |
* is not a supertype of the runtime type of every element in |
751 |
* this deque |
752 |
* @throws NullPointerException if the specified array is null |
753 |
*/ |
754 |
public <T> T[] toArray(T[] a) { |
755 |
int size = size(); |
756 |
if (a.length < size) |
757 |
a = (T[])java.lang.reflect.Array.newInstance( |
758 |
a.getClass().getComponentType(), size); |
759 |
copyElements(a); |
760 |
if (a.length > size) |
761 |
a[size] = null; |
762 |
return a; |
763 |
} |
764 |
|
765 |
// *** Object methods *** |
766 |
|
767 |
/** |
768 |
* Returns a copy of this deque. |
769 |
* |
770 |
* @return a copy of this deque |
771 |
*/ |
772 |
public ArrayDeque<E> clone() { |
773 |
try { |
774 |
ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); |
775 |
// These two lines are currently faster than cloning the array: |
776 |
result.elements = (E[]) new Object[elements.length]; |
777 |
System.arraycopy(elements, 0, result.elements, 0, elements.length); |
778 |
return result; |
779 |
|
780 |
} catch (CloneNotSupportedException e) { |
781 |
throw new AssertionError(); |
782 |
} |
783 |
} |
784 |
|
785 |
/** |
786 |
* Appease the serialization gods. |
787 |
*/ |
788 |
private static final long serialVersionUID = 2340985798034038923L; |
789 |
|
790 |
/** |
791 |
* Serialize this deque. |
792 |
* |
793 |
* @serialData The current size (<tt>int</tt>) of the deque, |
794 |
* followed by all of its elements (each an object reference) in |
795 |
* first-to-last order. |
796 |
*/ |
797 |
private void writeObject(ObjectOutputStream s) throws IOException { |
798 |
s.defaultWriteObject(); |
799 |
|
800 |
// Write out size |
801 |
int size = size(); |
802 |
s.writeInt(size); |
803 |
|
804 |
// Write out elements in order. |
805 |
int i = head; |
806 |
int mask = elements.length - 1; |
807 |
for (int j = 0; j < size; j++) { |
808 |
s.writeObject(elements[i]); |
809 |
i = (i + 1) & mask; |
810 |
} |
811 |
} |
812 |
|
813 |
/** |
814 |
* Deserialize this deque. |
815 |
*/ |
816 |
private void readObject(ObjectInputStream s) |
817 |
throws IOException, ClassNotFoundException { |
818 |
s.defaultReadObject(); |
819 |
|
820 |
// Read in size and allocate array |
821 |
int size = s.readInt(); |
822 |
allocateElements(size); |
823 |
head = 0; |
824 |
tail = size; |
825 |
|
826 |
// Read in all elements in the proper order. |
827 |
for (int i = 0; i < size; i++) |
828 |
elements[i] = (E)s.readObject(); |
829 |
|
830 |
} |
831 |
} |